ON AUGUST 31, 1998, two suspected cases of fungal pneumonia were reported to the Boulder County (Colorado) Health Department (BCHD). Both patients were immunocompetent, otherwise healthy adults working for the City of Boulder Open Space (CBOS) program on a prairie dog relocation project. This report summarizes the epidemiologic investigation by BCHD, the Colorado Department of Public Health and Environment, and CDC; the findings indicate that these two persons acquired blastomycosis in Colorado, which is outside the area where the disease is endemic.

Case Investigations

Patient 1.

On August 28, a 25-year-old man was admitted to a hospital with a 12-day history of fever, weight loss, fatigue, arthralgias, and productive cough. He had been treated by a private physician with two antibiotics during the preceding 8 days. On hospital admission, a computed tomography (CT) scan demonstrated bilateral pulmonary diffuse nodular opacities. A subsequent open lung biopsy revealed small budding yeasts. After 10 days of culture, Blastomyces dermatitidis was identified and confirmed by DNA probe (GenProbe, San Diego, California*), both at the local hospital laboratory and at CDC. The patient was treated with intravenous (IV) amphotericin B for 10 days, followed by a prescribed 6-month course of oral itraconazole.

Patient 2.

On September 3, a 35-year-old man sought care for a 15-day history of fever, fatigue, shortness of breath, arthralgias, skin lesions (punctate lesions on arms and trunk and lesions resembling erythema nodosum on legs), cough, chest pain, and weight loss. His symptoms did not improve after 9 days of treatment with two antibiotics, and he was admitted to the same hospital as patient 1. A CT scan revealed diffuse, bilateral pulmonary nodules. The consulting physician for this patient also had seen patient 1; on the basis of work history and clinical course of the disease, the consultant suspected a fungal pneumonia. Specimens obtained by transbronchial biopsy/lavage were negative for fungal elements by microscopic examination and culture. Open lung biopsy specimens revealed small budding yeasts morphologically indistinguishable from those found in patient 1. Biopsy specimens grew B. dermatitidis after 21 days of culture. The patient received IV amphotericin B for 14 days, and at discharge, a 6-month prescribed course of oral itraconazole.

Follow-Up Investigation

The two ill persons had worked together on the prairie dog relocation project on August 3 and 10 (14 and 7 days before onset of illness for patient 1). Work practices at the relocation site included using a gasoline-powered auger and hand trowels to excavate abandoned prairie dog tunnels and burrows that were being used by many other animal species. The workers did not use personal protective equipment (e.g., protective clothing or face masks). All 15 workers involved in the project were interviewed. The two ill persons had performed vigorous digging, created large amounts of dust, and spent 6-7 hours each day with their faces close to the dirt. It rained on 13 of the 15 days during July 22-August 5 (Colorado State University Climate Center, unpublished data, 1998); Boulder received 4.4 inches of rain during this period (normal rainfall for July and August combined is 3.3 inches).

The 15 workers were interviewed for symptoms of disease, and chest radiographs were offered to all workers; 12 (including the two ill workers) received chest radiographs. Only the two ill persons had chest abnormalities; both previously had lived in areas where the disease is endemic and where they could have been exposed to B. dermatitidis, but neither reported a history of such illness. Persons describing any symptoms of disease were referred to an occupational health specialist for further evaluation. Blood from 14 workers (including the two ill workers) was submitted for serologic testing (e.g., complement fixation, immunodiffusion, and radioimmunoassay)1; results are pending. CDC collected composite soil samples from burrows at the site for microbiologic analyses2; results are pending.

This article describes the first reported cases of blastomycosis acquired in Colorado. Blastomycosis is caused by inhalation of spores from B. dermatitidis, a dimorphic fungus found in soil and rotting wood. Blastomycosis most commonly presents as a subacute pulmonary disease, but the clinical spectrum ranges from asymptomatic infection to disseminated disease involving the skin, bones, and genitourinary system.3,4 In the United States, disease occurs sporadically throughout the Ohio and Mississippi river valleys and the southeastern states.5 In states where blastomycosis is reportable (e.g., Wisconsin and Mississippi), the annual incidence of disease is 1.3-1.4 per 100,000 population; in areas where it is endemic, smaller areas of hyperendemicity can have rates of up to 41.9 cases per 100,000 persons.6,7

In areas where blastomycosis is endemic, dogs infected with B. dermatitidis can signal increased risk for human infection.5 Few cases of blastomycosis have been reported among humans or animals in Colorado.8,9 Although both patients in this outbreak previously resided in areas where they could have been exposed to B. dermatitidis, it is unlikely that they would have concurrent reactivation of previously acquired disease.

Two factors may have contributed to blastomycosis in the two workers described in this report. First, B. dermatitidis is more common in soils with high nitrogen and organic content, which may have been provided by the stored food and fecal matter of the animals living in the burrows.2 Second, the above-average rainfall before the excavations may have been a factor, because humidity may aid reproduction of the organism.4

Blastomycosis should be considered in the differential diagnosis of illness in patients with subacute lobar or segmental pneumonia, particularly when it is refractory to initial antibiotic therapy and the patient has a history of outdoor occupational or recreational exposures. Serologic testing may assist in diagnosis, but complement fixation and immunodiffusion lack sensitivity and the WI-1 antigen-based antibody test has good sensitivity and specificity but is not widely available. Skin testing is not available for blastomycosis.4 Treatment of this disease includes ketoconazole or itraconazole for mild or moderate disease and intravenous amphotericin B for patients who are severely immunocompromised, have central nervous system involvement, or are severely ill.

The risk for exposure to blastomycosis remains small even in areas where the disease is endemic, and few public health recommendations have been developed for prevention of blastomycosis. Measures recommended for protecting workers against other endemic mycoses (e.g., histoplasmosis and coccidioidomycosis) probably will be protective against exposures to soil contaminated by B. dermatitidis.10 These measures include (1) use of a CDC-approved N-95 disposable half-facepiece filtering respirator (or equivalent) and protective clothing and shoe covers by all persons engaged in soil-disturbing activities during prairie dog relocation, (2) employer-provided instruction of all persons with potential to be engaged in these activities in the proper fitting and wearing of the recommended face mask, (3) implementation of a respiratory-protection program for employees, and (4) education of workers about clinical signs and symptoms of disease and screening and treatment options. Interim recommendations for workers engaged in prairie dog relocation have been developed by BCHD and will be modified as needed based on the serology and soil-testing results.

MMWR. 1999;48:98-100

*Use of trade names and commercial sources is for identification only and does not imply endorsement by CDC or the U.S. Department of Health and Human Services.